diff --git a/Taskfile.yaml b/Taskfile.yaml
index e713a4d..7834246 100644
--- a/Taskfile.yaml
+++ b/Taskfile.yaml
@@ -39,10 +39,10 @@ tasks:
     cmds:
       - "{{.GOLANGCI}} run"
 
-  test:
-    desc: Run Go tests.
+  e2e:
+    desc: Run e2e tests
     cmds:
-      - go test ./... {{.CLI_ARGS}}
+      - go test ./e2e/... -v -count=1 {{.CLI_ARGS}}
 
   create-bin-dir:
     desc: Create bin directory.
diff --git a/benchmark.sh b/benchmark.sh
new file mode 100755
index 0000000..b4c33cd
--- /dev/null
+++ b/benchmark.sh
@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+RUNS=20
+CMD="go run ./cmd/cli -U http://localhost:80 -r 1_000_000 -c 100"
+
+declare -a times_default
+declare -a times_gogcoff
+
+echo "===== Benchmark: default GC ====="
+for i in $(seq 1 $RUNS); do
+    echo "Run $i/$RUNS ..."
+    start=$(date +%s%N)
+    $CMD
+    end=$(date +%s%N)
+    elapsed=$(( (end - start) / 1000000 )) # milliseconds
+    times_default+=("$elapsed")
+    echo "  -> ${elapsed} ms"
+done
+
+echo ""
+echo "===== Benchmark: GOGC=off ====="
+for i in $(seq 1 $RUNS); do
+    echo "Run $i/$RUNS ..."
+    start=$(date +%s%N)
+    GOGC=off $CMD
+    end=$(date +%s%N)
+    elapsed=$(( (end - start) / 1000000 ))
+    times_gogcoff+=("$elapsed")
+    echo "  -> ${elapsed} ms"
+done
+
+echo ""
+echo "============================================"
+echo "                 RESULTS"
+echo "============================================"
+
+echo ""
+echo "--- Default GC ---"
+sum=0
+for i in $(seq 0 $((RUNS - 1))); do
+    echo "  Run $((i + 1)): ${times_default[$i]} ms"
+    sum=$((sum + times_default[$i]))
+done
+avg_default=$((sum / RUNS))
+echo "  Average: ${avg_default} ms"
+
+echo ""
+echo "--- GOGC=off ---"
+sum=0
+for i in $(seq 0 $((RUNS - 1))); do
+    echo "  Run $((i + 1)): ${times_gogcoff[$i]} ms"
+    sum=$((sum + times_gogcoff[$i]))
+done
+avg_gogcoff=$((sum / RUNS))
+echo "  Average: ${avg_gogcoff} ms"
+
+echo ""
+echo "--- Comparison ---"
+if [ "$avg_default" -gt 0 ]; then
+    diff=$((avg_default - avg_gogcoff))
+    echo "  Difference: ${diff} ms (positive = GOGC=off is faster)"
+fi
+echo "============================================"
diff --git a/e2e/basic_test.go b/e2e/basic_test.go
new file mode 100644
index 0000000..5e856aa
--- /dev/null
+++ b/e2e/basic_test.go
@@ -0,0 +1,220 @@
+package e2e
+
+import (
+	"strconv"
+	"testing"
+)
+
+func TestNoArgs(t *testing.T) {
+	t.Parallel()
+	res := run()
+	assertExitCode(t, res, 1)
+	// With no args and no env vars, validation should fail on required fields
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestHelp(t *testing.T) {
+	t.Parallel()
+	for _, flag := range []string{"-h", "-help"} {
+		t.Run(flag, func(t *testing.T) {
+			t.Parallel()
+			res := run(flag)
+			assertContains(t, res.Stdout, "Usage:")
+			assertContains(t, res.Stdout, "-url")
+		})
+	}
+}
+
+func TestVersion(t *testing.T) {
+	t.Parallel()
+	for _, flag := range []string{"-v", "-version"} {
+		t.Run(flag, func(t *testing.T) {
+			t.Parallel()
+			res := run(flag)
+			assertExitCode(t, res, 0)
+			assertContains(t, res.Stdout, "Version:")
+			assertContains(t, res.Stdout, "Git Commit:")
+		})
+	}
+}
+
+func TestUnexpectedArgs(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "unexpected")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "Unexpected CLI arguments")
+}
+
+func TestSimpleRequest(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-r", "3", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+	assertResponseCount(t, out, 3)
+}
+
+func TestDryRun(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "5", "-q", "-o", "json", "-z")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "dry-run")
+	assertResponseCount(t, out, 5)
+}
+
+func TestDryRunDoesNotSendRequests(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "5", "-q", "-o", "json", "-z")
+	assertExitCode(t, res, 0)
+
+	if cs.requestCount() != 0 {
+		t.Errorf("dry-run should not send any requests, but server received %d", cs.requestCount())
+	}
+}
+
+func TestQuietMode(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	if res.Stderr != "" {
+		t.Errorf("expected empty stderr in quiet mode, got: %s", res.Stderr)
+	}
+}
+
+func TestOutputNone(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-r", "1", "-q", "-o", "none")
+	assertExitCode(t, res, 0)
+
+	if res.Stdout != "" {
+		t.Errorf("expected empty stdout with -o none, got: %s", res.Stdout)
+	}
+}
+
+func TestOutputJSON(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	if out.Responses == nil {
+		t.Fatal("responses field is nil")
+	}
+	if out.Total.Min == "" || out.Total.Max == "" || out.Total.Average == "" {
+		t.Errorf("total stats are incomplete: %+v", out.Total)
+	}
+	if out.Total.P90 == "" || out.Total.P95 == "" || out.Total.P99 == "" {
+		t.Errorf("total percentiles are incomplete: %+v", out.Total)
+	}
+}
+
+func TestOutputYAML(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-r", "1", "-q", "-o", "yaml")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "responses:")
+	assertContains(t, res.Stdout, "total:")
+	assertContains(t, res.Stdout, "count:")
+}
+
+func TestOutputTable(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-r", "1", "-q", "-o", "table")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "Response")
+	assertContains(t, res.Stdout, "Count")
+	assertContains(t, res.Stdout, "Min")
+	assertContains(t, res.Stdout, "P99")
+}
+
+func TestInvalidOutputFormat(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1", "-o", "invalid")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "Output")
+}
+
+func TestStatusCodes(t *testing.T) {
+	t.Parallel()
+	codes := []int{200, 201, 204, 301, 400, 404, 500, 502}
+	for _, code := range codes {
+		t.Run(strconv.Itoa(code), func(t *testing.T) {
+			t.Parallel()
+			srv := statusServer(code)
+			defer srv.Close()
+
+			res := run("-U", srv.URL, "-r", "1", "-q", "-o", "json")
+			assertExitCode(t, res, 0)
+
+			out := res.jsonOutput(t)
+			assertHasResponseKey(t, out, strconv.Itoa(code))
+		})
+	}
+}
+
+func TestConcurrency(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-r", "10", "-c", "5", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertResponseCount(t, out, 10)
+}
+
+func TestDuration(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-d", "1s", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	count, _ := out.Total.Count.Int64()
+	if count < 1 {
+		t.Errorf("expected at least 1 request during 1s duration, got %d", count)
+	}
+}
+
+func TestRequestsAndDuration(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	// Both -r and -d set: should stop at whichever comes first
+	res := run("-U", srv.URL, "-r", "3", "-d", "10s", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertResponseCount(t, out, 3)
+}
diff --git a/e2e/config_file_test.go b/e2e/config_file_test.go
new file mode 100644
index 0000000..324012e
--- /dev/null
+++ b/e2e/config_file_test.go
@@ -0,0 +1,401 @@
+package e2e
+
+import (
+	"net/http"
+	"testing"
+)
+
+func TestConfigFileBasic(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+	assertResponseCount(t, out, 1)
+}
+
+func TestConfigFileWithMethod(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+method: POST
+requests: 1
+quiet: true
+output: json
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Method != http.MethodPost {
+		t.Errorf("expected method POST from config, got %s", req.Method)
+	}
+}
+
+func TestConfigFileWithHeaders(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+headers:
+  - X-Config: config-value
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Config"]; len(v) == 0 || v[0] != "config-value" {
+		t.Errorf("expected X-Config: config-value, got %v", v)
+	}
+}
+
+func TestConfigFileWithParams(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+params:
+  - key1: value1
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Query["key1"]; len(v) == 0 || v[0] != "value1" {
+		t.Errorf("expected key1=value1, got %v", v)
+	}
+}
+
+func TestConfigFileWithCookies(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+cookies:
+  - session: abc123
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Cookies["session"]; !ok || v != "abc123" {
+		t.Errorf("expected cookie session=abc123, got %v", req.Cookies)
+	}
+}
+
+func TestConfigFileWithBody(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+method: POST
+requests: 1
+quiet: true
+output: json
+body: "hello from config"
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "hello from config" {
+		t.Errorf("expected body 'hello from config', got %q", req.Body)
+	}
+}
+
+func TestConfigFileCLIOverridesScalars(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "http://should-be-overridden.invalid"
+requests: 1
+quiet: true
+output: json
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	// CLI -U should override the config file URL (scalar override)
+	res := run("-f", configPath, "-U", cs.URL)
+	assertExitCode(t, res, 0)
+	assertResponseCount(t, res.jsonOutput(t), 1)
+
+	// Verify it actually hit our server
+	if cs.requestCount() != 1 {
+		t.Errorf("expected 1 request to capture server, got %d", cs.requestCount())
+	}
+}
+
+func TestConfigFileCLIOverridesMethods(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+method: GET
+requests: 4
+quiet: true
+output: json
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	// CLI -M POST overrides config file's method: GET
+	res := run("-f", configPath, "-M", "POST")
+	assertExitCode(t, res, 0)
+
+	for _, r := range cs.allRequests() {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected all requests to be POST (CLI overrides config), got %s", r.Method)
+		}
+	}
+}
+
+func TestConfigFileInvalidYAML(t *testing.T) {
+	t.Parallel()
+	configPath := writeTemp(t, "bad.yaml", `{{{not valid yaml`)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 1)
+}
+
+func TestConfigFileNotFound(t *testing.T) {
+	t.Parallel()
+	res := run("-f", "/nonexistent/path/config.yaml")
+	assertExitCode(t, res, 1)
+}
+
+func TestConfigFileWithDryRun(t *testing.T) {
+	t.Parallel()
+
+	config := `
+url: "http://example.com"
+requests: 3
+quiet: true
+output: json
+dryRun: true
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "dry-run")
+	assertResponseCount(t, out, 3)
+}
+
+func TestConfigFileWithConcurrency(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 6
+concurrency: 3
+quiet: true
+output: json
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertResponseCount(t, out, 6)
+}
+
+func TestConfigFileNestedIncludes(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Create inner config
+	innerConfig := `
+headers:
+  - X-Inner: from-inner
+`
+	innerPath := writeTemp(t, "inner.yaml", innerConfig)
+
+	// Create outer config that includes inner
+	outerConfig := `
+configFile: "` + innerPath + `"
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+`
+	outerPath := writeTemp(t, "outer.yaml", outerConfig)
+
+	res := run("-f", outerPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Inner"]; len(v) == 0 || v[0] != "from-inner" {
+		t.Errorf("expected X-Inner: from-inner from nested config, got %v", v)
+	}
+}
+
+func TestConfigFileFromHTTPURL(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+headers:
+  - X-Remote-Config: yes
+`
+	// Serve config via HTTP
+	configServer := statusServerWithBody(config)
+	defer configServer.Close()
+
+	res := run("-f", configServer.URL)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Remote-Config"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-Remote-Config: yes from HTTP config, got %v", v)
+	}
+}
+
+func TestConfigFileMultiValueHeaders(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+headers:
+  - X-Multi:
+    - val1
+    - val2
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	// With multiple values, sarin cycles through them (random start).
+	// With -r 1, we should see exactly one of them.
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	v, ok := req.Headers["X-Multi"]
+	if !ok || len(v) == 0 {
+		t.Fatalf("expected X-Multi header, got headers: %v", req.Headers)
+	}
+	if v[0] != "val1" && v[0] != "val2" {
+		t.Errorf("expected X-Multi to be val1 or val2, got %v", v)
+	}
+}
+
+func TestConfigFileWithTimeout(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+timeout: 5s
+quiet: true
+output: json
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+	assertResponseCount(t, res.jsonOutput(t), 1)
+}
+
+func TestConfigFileWithInsecure(t *testing.T) {
+	t.Parallel()
+
+	config := `
+url: "http://example.com"
+requests: 1
+insecure: true
+quiet: true
+output: json
+dryRun: true
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+}
+
+func TestConfigFileWithLuaScript(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	scriptContent := `function transform(req) req.headers["X-Config-Lua"] = {"yes"} return req end`
+	scriptPath := writeTemp(t, "script.lua", scriptContent)
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+lua: "@` + scriptPath + `"
+`
+	configPath := writeTemp(t, "config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Config-Lua"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-Config-Lua: yes, got %v", v)
+	}
+}
diff --git a/e2e/config_merge_test.go b/e2e/config_merge_test.go
new file mode 100644
index 0000000..1822702
--- /dev/null
+++ b/e2e/config_merge_test.go
@@ -0,0 +1,282 @@
+package e2e
+
+import (
+	"net/http"
+	"testing"
+)
+
+// --- Multiple config files ---
+
+func TestMultipleConfigFiles(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config1 := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+headers:
+  - X-From-File1: yes
+`
+	config2 := `
+headers:
+  - X-From-File2: yes
+`
+	path1 := writeTemp(t, "merge1.yaml", config1)
+	path2 := writeTemp(t, "merge2.yaml", config2)
+
+	res := run("-f", path1, "-f", path2)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-From-File1"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-From-File1: yes, got %v", v)
+	}
+	if v := req.Headers["X-From-File2"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-From-File2: yes, got %v", v)
+	}
+}
+
+func TestMultipleConfigFilesScalarOverride(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Second config file overrides URL from first
+	config1 := `
+url: "http://should-be-overridden.invalid"
+requests: 1
+quiet: true
+output: json
+`
+	config2 := `
+url: "` + cs.URL + `"
+`
+	path1 := writeTemp(t, "merge_scalar1.yaml", config1)
+	path2 := writeTemp(t, "merge_scalar2.yaml", config2)
+
+	res := run("-f", path1, "-f", path2)
+	assertExitCode(t, res, 0)
+
+	if cs.requestCount() != 1 {
+		t.Errorf("expected request to go to second config's URL, got %d requests", cs.requestCount())
+	}
+}
+
+// --- Three-way merge: env + config file + CLI ---
+
+func TestThreeWayMergePriority(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+method: PUT
+headers:
+  - X-From-Config: config-value
+`
+	configPath := writeTemp(t, "three_way.yaml", config)
+
+	// ENV sets URL and header, config file sets method and header, CLI overrides URL
+	res := runWithEnv(map[string]string{
+		"SARIN_HEADER": "X-From-Env: env-value",
+	}, "-U", cs.URL, "-r", "1", "-q", "-o", "json", "-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	// Method should be PUT from config (not default GET)
+	if req.Method != http.MethodPut {
+		t.Errorf("expected method PUT from config, got %s", req.Method)
+	}
+	// Header from config file should be present
+	if v := req.Headers["X-From-Config"]; len(v) == 0 || v[0] != "config-value" {
+		t.Errorf("expected X-From-Config from config file, got %v", v)
+	}
+	// Header from env should be present
+	if v := req.Headers["X-From-Env"]; len(v) == 0 || v[0] != "env-value" {
+		t.Errorf("expected X-From-Env from env, got %v", v)
+	}
+}
+
+// --- Config file nesting depth ---
+
+func TestConfigFileNestedMaxDepth(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Create a chain of 12 config files (exceeds max depth of 10)
+	// The innermost file has the actual URL config
+	// When depth is exceeded, inner files are silently ignored
+
+	files := make([]string, 12)
+
+	// Innermost file (index 11) - has the real config
+	files[11] = writeTemp(t, "depth11.yaml", `
+url: "`+cs.URL+`"
+requests: 1
+quiet: true
+output: json
+headers:
+  - X-Depth: deep
+`)
+
+	// Chain each file to include the next one
+	for i := 10; i >= 0; i-- {
+		content := `configFile: "` + files[i+1] + `"`
+		files[i] = writeTemp(t, "depth"+string(rune('0'+i))+".yaml", content)
+	}
+
+	// The outermost file: this will recurse but max depth will prevent
+	// reaching the innermost file with the URL
+	res := run("-f", files[0], "-q")
+	// This should fail because URL is never reached (too deep)
+	assertExitCode(t, res, 1)
+}
+
+// --- YAML format flexibility ---
+
+func TestConfigFileParamsMapFormat(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+params:
+  key1: value1
+  key2: value2
+`
+	configPath := writeTemp(t, "params_map.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Query["key1"]; len(v) == 0 || v[0] != "value1" {
+		t.Errorf("expected key1=value1, got %v", v)
+	}
+	if v := req.Query["key2"]; len(v) == 0 || v[0] != "value2" {
+		t.Errorf("expected key2=value2, got %v", v)
+	}
+}
+
+func TestConfigFileHeadersMapFormat(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+headers:
+  X-Map-A: map-val-a
+  X-Map-B: map-val-b
+`
+	configPath := writeTemp(t, "headers_map.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Map-A"]; len(v) == 0 || v[0] != "map-val-a" {
+		t.Errorf("expected X-Map-A: map-val-a, got %v", v)
+	}
+	if v := req.Headers["X-Map-B"]; len(v) == 0 || v[0] != "map-val-b" {
+		t.Errorf("expected X-Map-B: map-val-b, got %v", v)
+	}
+}
+
+func TestConfigFileCookiesMapFormat(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+cookies:
+  sess: abc
+  token: xyz
+`
+	configPath := writeTemp(t, "cookies_map.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Cookies["sess"]; !ok || v != "abc" {
+		t.Errorf("expected cookie sess=abc, got %v", req.Cookies)
+	}
+	if v, ok := req.Cookies["token"]; !ok || v != "xyz" {
+		t.Errorf("expected cookie token=xyz, got %v", req.Cookies)
+	}
+}
+
+func TestConfigFileMultipleBodies(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 10
+concurrency: 1
+method: POST
+quiet: true
+output: json
+body:
+  - "body-one"
+  - "body-two"
+`
+	configPath := writeTemp(t, "multi_body.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	bodies := map[string]bool{}
+	for _, req := range cs.allRequests() {
+		bodies[req.Body] = true
+	}
+	if !bodies["body-one"] || !bodies["body-two"] {
+		t.Errorf("expected both body-one and body-two to appear, got %v", bodies)
+	}
+}
+
+func TestConfigFileMultipleMethods(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 10
+concurrency: 1
+quiet: true
+output: json
+method:
+  - GET
+  - POST
+`
+	configPath := writeTemp(t, "multi_method.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	methods := map[string]bool{}
+	for _, req := range cs.allRequests() {
+		methods[req.Method] = true
+	}
+	if !methods["GET"] || !methods["POST"] {
+		t.Errorf("expected both GET and POST, got %v", methods)
+	}
+}
diff --git a/e2e/config_nested_http_test.go b/e2e/config_nested_http_test.go
new file mode 100644
index 0000000..ef3727e
--- /dev/null
+++ b/e2e/config_nested_http_test.go
@@ -0,0 +1,37 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestConfigFileNestedHTTPInclude(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Inner config served via HTTP
+	innerConfig := `
+headers:
+  - X-From-HTTP-Nested: yes
+`
+	innerServer := statusServerWithBody(innerConfig)
+	defer innerServer.Close()
+
+	// Outer config references the inner config via HTTP URL
+	outerConfig := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+configFile: "` + innerServer.URL + `"
+`
+	outerPath := writeTemp(t, "outer_http.yaml", outerConfig)
+
+	res := run("-f", outerPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-From-Http-Nested"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-From-Http-Nested: yes from nested HTTP config, got %v", v)
+	}
+}
diff --git a/e2e/e2e_test.go b/e2e/e2e_test.go
new file mode 100644
index 0000000..0f15936
--- /dev/null
+++ b/e2e/e2e_test.go
@@ -0,0 +1,316 @@
+package e2e
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+var binaryPath string
+
+func TestMain(m *testing.M) {
+	// Build the binary once before all tests.
+	tmpDir, err := os.MkdirTemp("", "sarin-e2e-*")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "failed to create temp dir: %v\n", err)
+		os.Exit(1)
+	}
+	binaryPath = filepath.Join(tmpDir, "sarin")
+	if runtime.GOOS == "windows" {
+		binaryPath += ".exe"
+	}
+
+	cmd := exec.Command("go", "build", "-o", binaryPath, "../cmd/cli/main.go")
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		fmt.Fprintf(os.Stderr, "failed to build binary: %v\n", err)
+		os.Exit(1)
+	}
+
+	code := m.Run()
+	os.RemoveAll(tmpDir)
+	os.Exit(code)
+}
+
+// --- Result type ---
+
+// runResult holds the output of a sarin binary execution.
+type runResult struct {
+	Stdout   string
+	Stderr   string
+	ExitCode int
+}
+
+// jsonOutput parses the stdout as JSON output from sarin.
+// Fails the test if parsing fails.
+func (r runResult) jsonOutput(t *testing.T) outputData {
+	t.Helper()
+	var out outputData
+	if err := json.Unmarshal([]byte(r.Stdout), &out); err != nil {
+		t.Fatalf("failed to parse JSON output: %v\nstdout: %s", err, r.Stdout)
+	}
+	return out
+}
+
+// --- JSON output structures ---
+
+type responseStat struct {
+	Count   json.Number `json:"count"`
+	Min     string      `json:"min"`
+	Max     string      `json:"max"`
+	Average string      `json:"average"`
+	P90     string      `json:"p90"`
+	P95     string      `json:"p95"`
+	P99     string      `json:"p99"`
+}
+
+type outputData struct {
+	Responses map[string]responseStat `json:"responses"`
+	Total     responseStat            `json:"total"`
+}
+
+// --- echoResponse is the JSON structure returned by echoServer ---
+
+type echoResponse struct {
+	Method  string              `json:"method"`
+	Path    string              `json:"path"`
+	Query   map[string][]string `json:"query"`
+	Headers map[string][]string `json:"headers"`
+	Cookies map[string]string   `json:"cookies"`
+	Body    string              `json:"body"`
+}
+
+// --- Helpers ---
+
+// run executes the sarin binary with the given args and returns the result.
+func run(args ...string) runResult {
+	cmd := exec.Command(binaryPath, args...)
+	var stdout, stderr strings.Builder
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+
+	err := cmd.Run()
+	exitCode := 0
+	if err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			exitCode = exitErr.ExitCode()
+		} else {
+			exitCode = -1
+		}
+	}
+
+	return runResult{
+		Stdout:   stdout.String(),
+		Stderr:   stderr.String(),
+		ExitCode: exitCode,
+	}
+}
+
+// runWithEnv executes the sarin binary with the given args and environment variables.
+func runWithEnv(env map[string]string, args ...string) runResult {
+	cmd := exec.Command(binaryPath, args...)
+	var stdout, stderr strings.Builder
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+
+	// Start with a clean env, then add the requested vars
+	cmd.Env = os.Environ()
+	for k, v := range env {
+		cmd.Env = append(cmd.Env, k+"="+v)
+	}
+
+	err := cmd.Run()
+	exitCode := 0
+	if err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			exitCode = exitErr.ExitCode()
+		} else {
+			exitCode = -1
+		}
+	}
+
+	return runResult{
+		Stdout:   stdout.String(),
+		Stderr:   stderr.String(),
+		ExitCode: exitCode,
+	}
+}
+
+// startProcess starts the sarin binary and returns the exec.Cmd without waiting.
+// The caller is responsible for managing the process lifecycle.
+func startProcess(args ...string) (*exec.Cmd, *strings.Builder) {
+	cmd := exec.Command(binaryPath, args...)
+	var stdout strings.Builder
+	cmd.Stdout = &stdout
+	return cmd, &stdout
+}
+
+// slowServer returns a server that delays each response by the given duration.
+func slowServer(delay time.Duration) *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		time.Sleep(delay)
+		w.WriteHeader(http.StatusOK)
+	}))
+}
+
+// echoServer starts an HTTP test server that echoes request details back as JSON.
+// The response includes method, path, headers, query params, cookies, and body.
+func echoServer() *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+
+		cookies := make(map[string]string)
+		for _, c := range r.Cookies() {
+			cookies[c.Name] = c.Value
+		}
+
+		resp := echoResponse{
+			Method:  r.Method,
+			Path:    r.URL.Path,
+			Query:   r.URL.Query(),
+			Headers: r.Header,
+			Cookies: cookies,
+			Body:    string(body),
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(resp)
+	}))
+}
+
+// captureServer records every request it receives and responds with 200.
+// Use lastRequest() to inspect the most recent request.
+type captureServer struct {
+	*httptest.Server
+
+	mu       sync.Mutex
+	requests []echoResponse
+}
+
+func newCaptureServer() *captureServer {
+	cs := &captureServer{}
+	cs.Server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+
+		cookies := make(map[string]string)
+		for _, c := range r.Cookies() {
+			cookies[c.Name] = c.Value
+		}
+
+		cs.mu.Lock()
+		cs.requests = append(cs.requests, echoResponse{
+			Method:  r.Method,
+			Path:    r.URL.Path,
+			Query:   r.URL.Query(),
+			Headers: r.Header,
+			Cookies: cookies,
+			Body:    string(body),
+		})
+		cs.mu.Unlock()
+
+		w.WriteHeader(http.StatusOK)
+	}))
+	return cs
+}
+
+func (cs *captureServer) lastRequest() echoResponse {
+	cs.mu.Lock()
+	defer cs.mu.Unlock()
+	if len(cs.requests) == 0 {
+		return echoResponse{}
+	}
+	return cs.requests[len(cs.requests)-1]
+}
+
+func (cs *captureServer) allRequests() []echoResponse {
+	cs.mu.Lock()
+	defer cs.mu.Unlock()
+	copied := make([]echoResponse, len(cs.requests))
+	copy(copied, cs.requests)
+	return copied
+}
+
+func (cs *captureServer) requestCount() int {
+	cs.mu.Lock()
+	defer cs.mu.Unlock()
+	return len(cs.requests)
+}
+
+// statusServer returns a server that always responds with the given status code.
+func statusServer(code int) *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(code)
+	}))
+}
+
+// statusServerWithBody returns a server that responds with 200 and the given body.
+func statusServerWithBody(body string) *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(body))
+	}))
+}
+
+// writeTemp creates a temporary file with the given content and returns its path.
+// The file is automatically cleaned up when the test finishes.
+func writeTemp(t *testing.T, name, content string) string {
+	t.Helper()
+	dir := t.TempDir()
+	path := filepath.Join(dir, name)
+	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		t.Fatalf("failed to write temp file: %v", err)
+	}
+	return path
+}
+
+// --- Assertion helpers ---
+
+func assertExitCode(t *testing.T, res runResult, want int) {
+	t.Helper()
+	if res.ExitCode != want {
+		t.Errorf("expected exit code %d, got %d\nstdout: %s\nstderr: %s", want, res.ExitCode, res.Stdout, res.Stderr)
+	}
+}
+
+func assertContains(t *testing.T, s, substr string) {
+	t.Helper()
+	if !strings.Contains(s, substr) {
+		t.Errorf("expected output to contain %q, got:\n%s", substr, s)
+	}
+}
+
+func assertResponseCount(t *testing.T, out outputData, wantTotal int) {
+	t.Helper()
+	got, err := out.Total.Count.Int64()
+	if err != nil {
+		t.Fatalf("failed to parse total count: %v", err)
+	}
+	if got != int64(wantTotal) {
+		t.Errorf("expected total count %d, got %d", wantTotal, got)
+	}
+}
+
+func assertHasResponseKey(t *testing.T, out outputData, key string) {
+	t.Helper()
+	if _, ok := out.Responses[key]; !ok {
+		t.Errorf("expected %q in responses, got keys: %v", key, responseKeys(out))
+	}
+}
+
+func responseKeys(out outputData) []string {
+	keys := make([]string, 0, len(out.Responses))
+	for k := range out.Responses {
+		keys = append(keys, k)
+	}
+	return keys
+}
diff --git a/e2e/env_errors_test.go b/e2e/env_errors_test.go
new file mode 100644
index 0000000..52835b3
--- /dev/null
+++ b/e2e/env_errors_test.go
@@ -0,0 +1,87 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestEnvInvalidConcurrency(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":         "http://example.com",
+		"SARIN_REQUESTS":    "1",
+		"SARIN_CONCURRENCY": "not-a-number",
+	}, "-q")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "invalid value for unsigned integer")
+}
+
+func TestEnvInvalidRequests(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "abc",
+	}, "-q")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "invalid value for unsigned integer")
+}
+
+func TestEnvInvalidDuration(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_DURATION": "not-a-duration",
+	}, "-q")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "invalid value duration")
+}
+
+func TestEnvInvalidTimeout(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "1",
+		"SARIN_TIMEOUT":  "xyz",
+	}, "-q")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "invalid value duration")
+}
+
+func TestEnvInvalidInsecure(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "1",
+		"SARIN_INSECURE": "maybe",
+	}, "-q")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "invalid value for boolean")
+}
+
+func TestEnvInvalidDryRun(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "1",
+		"SARIN_DRY_RUN":  "yes",
+	}, "-q")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "invalid value for boolean")
+}
+
+func TestEnvInvalidShowConfig(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":         "http://example.com",
+		"SARIN_REQUESTS":    "1",
+		"SARIN_SHOW_CONFIG": "nope",
+	}, "-q")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "invalid value for boolean")
+}
diff --git a/e2e/env_test.go b/e2e/env_test.go
new file mode 100644
index 0000000..8ca1d13
--- /dev/null
+++ b/e2e/env_test.go
@@ -0,0 +1,348 @@
+package e2e
+
+import (
+	"net/http"
+	"testing"
+)
+
+func TestEnvURL(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+	assertResponseCount(t, out, 1)
+}
+
+func TestEnvMethod(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_METHOD":   "POST",
+		"SARIN_REQUESTS": "1",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Method != http.MethodPost {
+		t.Errorf("expected method POST from env, got %s", req.Method)
+	}
+}
+
+func TestEnvConcurrency(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":         cs.URL,
+		"SARIN_REQUESTS":    "6",
+		"SARIN_CONCURRENCY": "3",
+		"SARIN_QUIET":       "true",
+		"SARIN_OUTPUT":      "json",
+	})
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertResponseCount(t, out, 6)
+}
+
+func TestEnvDuration(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_DURATION": "1s",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	count, _ := out.Total.Count.Int64()
+	if count < 1 {
+		t.Errorf("expected at least 1 request during 1s, got %d", count)
+	}
+}
+
+func TestEnvTimeout(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_TIMEOUT":  "5s",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+	assertResponseCount(t, res.jsonOutput(t), 1)
+}
+
+func TestEnvHeader(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_HEADER":   "X-From-Env: env-value",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-From-Env"]; len(v) == 0 || v[0] != "env-value" {
+		t.Errorf("expected X-From-Env: env-value, got %v", v)
+	}
+}
+
+func TestEnvParam(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_PARAM":    "env_key=env_val",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Query["env_key"]; len(v) == 0 || v[0] != "env_val" {
+		t.Errorf("expected env_key=env_val, got %v", v)
+	}
+}
+
+func TestEnvCookie(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_COOKIE":   "env_session=env_abc",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Cookies["env_session"]; !ok || v != "env_abc" {
+		t.Errorf("expected cookie env_session=env_abc, got %v", req.Cookies)
+	}
+}
+
+func TestEnvBody(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_METHOD":   "POST",
+		"SARIN_REQUESTS": "1",
+		"SARIN_BODY":     "env-body-content",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "env-body-content" {
+		t.Errorf("expected body 'env-body-content', got %q", req.Body)
+	}
+}
+
+func TestEnvDryRun(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "3",
+		"SARIN_DRY_RUN":  "true",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "dry-run")
+	assertResponseCount(t, out, 3)
+}
+
+func TestEnvInsecure(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "1",
+		"SARIN_INSECURE": "true",
+		"SARIN_DRY_RUN":  "true",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+}
+
+func TestEnvOutputNone(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "none",
+	})
+	assertExitCode(t, res, 0)
+
+	if res.Stdout != "" {
+		t.Errorf("expected empty stdout with output=none, got: %s", res.Stdout)
+	}
+}
+
+func TestEnvConfigFile(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 1
+quiet: true
+output: json
+headers:
+  - X-From-Env-Config: yes
+`
+	configPath := writeTemp(t, "env_config.yaml", config)
+
+	res := runWithEnv(map[string]string{
+		"SARIN_CONFIG_FILE": configPath,
+	})
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-From-Env-Config"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-From-Env-Config: yes, got %v", v)
+	}
+}
+
+func TestEnvCLIOverridesEnv(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// CLI should take priority over env vars
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://should-be-overridden.invalid",
+		"SARIN_REQUESTS": "1",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	}, "-U", cs.URL)
+	assertExitCode(t, res, 0)
+
+	if cs.requestCount() != 1 {
+		t.Errorf("expected CLI URL to override env, but server got %d requests", cs.requestCount())
+	}
+}
+
+func TestEnvInvalidBool(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "1",
+		"SARIN_QUIET":    "not-a-bool",
+	})
+	assertExitCode(t, res, 1)
+}
+
+func TestEnvLuaScript(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) req.headers["X-Env-Lua"] = {"yes"} return req end`
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+		"SARIN_LUA":      script,
+	})
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Env-Lua"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-Env-Lua: yes, got %v", v)
+	}
+}
+
+func TestEnvJsScript(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) { req.headers["X-Env-Js"] = ["yes"]; return req; }`
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+		"SARIN_JS":       script,
+	})
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Env-Js"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-Env-Js: yes, got %v", v)
+	}
+}
+
+func TestEnvValues(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      cs.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+		"SARIN_VALUES":   "MY_KEY=my_val",
+	}, "-H", "X-Val: {{ .Values.MY_KEY }}")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Val"]; len(v) == 0 || v[0] != "my_val" {
+		t.Errorf("expected X-Val: my_val, got %v", v)
+	}
+}
diff --git a/e2e/formdata_test.go b/e2e/formdata_test.go
new file mode 100644
index 0000000..4360b4d
--- /dev/null
+++ b/e2e/formdata_test.go
@@ -0,0 +1,149 @@
+package e2e
+
+import (
+	"encoding/base64"
+	"testing"
+)
+
+func TestBodyFormDataSimple(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ body_FormData "name" "John" "age" "30" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	// Body should contain multipart form data
+	assertContains(t, req.Body, "name")
+	assertContains(t, req.Body, "John")
+	assertContains(t, req.Body, "age")
+	assertContains(t, req.Body, "30")
+
+	// Content-Type should be multipart/form-data
+	ct := req.Headers["Content-Type"]
+	if len(ct) == 0 {
+		t.Fatal("expected Content-Type header for form data")
+	}
+	assertContains(t, ct[0], "multipart/form-data")
+}
+
+func TestBodyFormDataWithFileUpload(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Create a temp file to upload
+	filePath := writeTemp(t, "upload.txt", "file content here")
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ body_FormData "description" "test file" "document" "@`+filePath+`" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	assertContains(t, req.Body, "description")
+	assertContains(t, req.Body, "test file")
+	assertContains(t, req.Body, "file content here")
+	assertContains(t, req.Body, "upload.txt")
+}
+
+func TestBodyFormDataWithRemoteFile(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Serve a file via HTTP
+	fileServer := statusServerWithBody("remote file content")
+	defer fileServer.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ body_FormData "file" "@`+fileServer.URL+`" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	assertContains(t, req.Body, "remote file content")
+}
+
+func TestBodyFormDataEscapedAt(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// @@ should send literal @ prefixed value
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ body_FormData "email" "@@user@example.com" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	assertContains(t, req.Body, "@user@example.com")
+}
+
+func TestBodyFormDataOddArgsError(t *testing.T) {
+	t.Parallel()
+
+	// Odd number of args should cause an error
+	res := run("-U", "http://example.com", "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ body_FormData "key_only" }}`)
+	// This should either fail at validation or produce an error in output
+	// The template is valid syntax but body_FormData returns an error at runtime
+	if res.ExitCode == 0 {
+		out := res.jsonOutput(t)
+		// If it didn't exit 1, the error should show up as a response key
+		if _, ok := out.Responses["200"]; ok {
+			t.Error("expected error for odd form data args, but got 200")
+		}
+	}
+}
+
+func TestFileBase64(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	content := "hello base64 world"
+	filePath := writeTemp(t, "base64test.txt", content)
+	expected := base64.StdEncoding.EncodeToString([]byte(content))
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ file_Base64 "`+filePath+`" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != expected {
+		t.Errorf("expected base64 %q, got %q", expected, req.Body)
+	}
+}
+
+func TestFileBase64RemoteFile(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	content := "remote base64 content"
+	fileServer := statusServerWithBody(content)
+	defer fileServer.Close()
+
+	expected := base64.StdEncoding.EncodeToString([]byte(content))
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ file_Base64 "`+fileServer.URL+`" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != expected {
+		t.Errorf("expected base64 %q, got %q", expected, req.Body)
+	}
+}
+
+func TestBodyFormDataMultipleRequests(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "3", "-c", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ body_FormData "id" "{{ fakeit_UUID }}" }}`)
+	assertExitCode(t, res, 0)
+
+	assertResponseCount(t, res.jsonOutput(t), 3)
+}
diff --git a/e2e/multi_value_test.go b/e2e/multi_value_test.go
new file mode 100644
index 0000000..15e4ba9
--- /dev/null
+++ b/e2e/multi_value_test.go
@@ -0,0 +1,226 @@
+package e2e
+
+import (
+	"net/http"
+	"testing"
+)
+
+// --- CLI: multiple same-key values are all sent in every request ---
+
+func TestMultipleHeadersSameKeyCLI(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-H", "X-Multi: value1", "-H", "X-Multi: value2")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	vals := req.Headers["X-Multi"]
+	if len(vals) < 2 {
+		t.Fatalf("expected 2 values for X-Multi, got %v", vals)
+	}
+	found := map[string]bool{}
+	for _, v := range vals {
+		found[v] = true
+	}
+	if !found["value1"] || !found["value2"] {
+		t.Errorf("expected both value1 and value2, got %v", vals)
+	}
+}
+
+func TestMultipleParamsSameKeyCLI(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-P", "color=red", "-P", "color=blue")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	vals := req.Query["color"]
+	if len(vals) < 2 {
+		t.Fatalf("expected 2 values for color param, got %v", vals)
+	}
+	found := map[string]bool{}
+	for _, v := range vals {
+		found[v] = true
+	}
+	if !found["red"] || !found["blue"] {
+		t.Errorf("expected both red and blue, got %v", vals)
+	}
+}
+
+func TestMultipleCookiesSameKeyCLI(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-C", "token=abc", "-C", "token=def")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	cookieHeader := ""
+	if v := req.Headers["Cookie"]; len(v) > 0 {
+		cookieHeader = v[0]
+	}
+	assertContains(t, cookieHeader, "token=abc")
+	assertContains(t, cookieHeader, "token=def")
+}
+
+// --- Config file: multiple values for same key cycle across requests ---
+
+func TestMultipleHeadersSameKeyYAMLCycle(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 20
+concurrency: 1
+quiet: true
+output: json
+headers:
+  - X-Multi: [val-a, val-b]
+`
+	configPath := writeTemp(t, "multi_header.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	seen := map[string]bool{}
+	for _, req := range cs.allRequests() {
+		if vals := req.Headers["X-Multi"]; len(vals) > 0 {
+			seen[vals[0]] = true
+		}
+	}
+	if !seen["val-a"] {
+		t.Error("expected val-a to appear in some requests")
+	}
+	if !seen["val-b"] {
+		t.Error("expected val-b to appear in some requests")
+	}
+}
+
+func TestMultipleParamsSameKeyYAMLCycle(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	config := `
+url: "` + cs.URL + `"
+requests: 20
+concurrency: 1
+quiet: true
+output: json
+params:
+  - tag: [go, rust]
+`
+	configPath := writeTemp(t, "multi_param.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	seen := map[string]bool{}
+	for _, req := range cs.allRequests() {
+		if vals := req.Query["tag"]; len(vals) > 0 {
+			seen[vals[0]] = true
+		}
+	}
+	if !seen["go"] {
+		t.Error("expected 'go' to appear in some requests")
+	}
+	if !seen["rust"] {
+		t.Error("expected 'rust' to appear in some requests")
+	}
+}
+
+// --- Multiple bodies cycle ---
+
+func TestMultipleBodiesCycle(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "10", "-c", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", "body-alpha", "-B", "body-beta")
+	assertExitCode(t, res, 0)
+
+	bodies := map[string]bool{}
+	for _, req := range cs.allRequests() {
+		bodies[req.Body] = true
+	}
+	if !bodies["body-alpha"] {
+		t.Error("expected body-alpha to appear in requests")
+	}
+	if !bodies["body-beta"] {
+		t.Error("expected body-beta to appear in requests")
+	}
+}
+
+// --- Multiple methods cycling ---
+
+func TestMultipleMethodsCycleDistribution(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "20", "-c", "1", "-q", "-o", "json",
+		"-M", "GET", "-M", "POST", "-M", "PUT")
+	assertExitCode(t, res, 0)
+
+	methods := map[string]int{}
+	for _, req := range cs.allRequests() {
+		methods[req.Method]++
+	}
+	if methods["GET"] == 0 {
+		t.Error("expected GET to appear")
+	}
+	if methods["POST"] == 0 {
+		t.Error("expected POST to appear")
+	}
+	if methods["PUT"] == 0 {
+		t.Error("expected PUT to appear")
+	}
+}
+
+// --- Template in method ---
+
+func TestTemplateInMethod(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-M", `{{ strings_ToUpper "post" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Method != http.MethodPost {
+		t.Errorf("expected method POST from template, got %s", req.Method)
+	}
+}
+
+// --- Template in cookie value ---
+
+func TestTemplateInCookie(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-C", `session={{ fakeit_UUID }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Cookies["session"] == "" {
+		t.Error("expected session cookie with UUID value, got empty")
+	}
+	if len(req.Cookies["session"]) < 10 {
+		t.Errorf("expected UUID-like session cookie, got %q", req.Cookies["session"])
+	}
+}
diff --git a/e2e/output_test.go b/e2e/output_test.go
new file mode 100644
index 0000000..1231b67
--- /dev/null
+++ b/e2e/output_test.go
@@ -0,0 +1,198 @@
+package e2e
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"go.yaml.in/yaml/v4"
+)
+
+// --- JSON output structure verification ---
+
+func TestJSONOutputHasStatFields(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "3", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+
+	// Verify total has all stat fields
+	if out.Total.Count.String() != "3" {
+		t.Errorf("expected count 3, got %s", out.Total.Count.String())
+	}
+	if out.Total.Min == "" {
+		t.Error("expected min to be non-empty")
+	}
+	if out.Total.Max == "" {
+		t.Error("expected max to be non-empty")
+	}
+	if out.Total.Average == "" {
+		t.Error("expected average to be non-empty")
+	}
+	if out.Total.P90 == "" {
+		t.Error("expected p90 to be non-empty")
+	}
+	if out.Total.P95 == "" {
+		t.Error("expected p95 to be non-empty")
+	}
+	if out.Total.P99 == "" {
+		t.Error("expected p99 to be non-empty")
+	}
+}
+
+func TestJSONOutputResponseStatFields(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "5", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	stat, ok := out.Responses["200"]
+	if !ok {
+		t.Fatal("expected 200 in responses")
+	}
+
+	if stat.Count.String() != "5" {
+		t.Errorf("expected response count 5, got %s", stat.Count.String())
+	}
+	if stat.Min == "" || stat.Max == "" || stat.Average == "" {
+		t.Error("expected min/max/average to be non-empty")
+	}
+}
+
+func TestJSONOutputMultipleStatusCodes(t *testing.T) {
+	t.Parallel()
+
+	// Create servers with different status codes
+	srv200 := statusServer(200)
+	defer srv200.Close()
+	srv404 := statusServer(404)
+	defer srv404.Close()
+
+	// We can only target one URL, so use a single server
+	// Instead, test that dry-run produces the expected structure
+	res := run("-U", "http://example.com", "-r", "3", "-z", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	// dry-run should have "dry-run" key
+	stat := out.Responses["dry-run"]
+	if stat.Count.String() != "3" {
+		t.Errorf("expected dry-run count 3, got %s", stat.Count.String())
+	}
+}
+
+func TestJSONOutputIsValidJSON(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	// Verify it's valid JSON
+	var raw map[string]any
+	if err := json.Unmarshal([]byte(res.Stdout), &raw); err != nil {
+		t.Fatalf("stdout is not valid JSON: %v", err)
+	}
+
+	// Verify top-level structure
+	if _, ok := raw["responses"]; !ok {
+		t.Error("expected 'responses' key in JSON output")
+	}
+	if _, ok := raw["total"]; !ok {
+		t.Error("expected 'total' key in JSON output")
+	}
+}
+
+// --- YAML output structure verification ---
+
+func TestYAMLOutputIsValidYAML(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "yaml")
+	assertExitCode(t, res, 0)
+
+	var raw map[string]any
+	if err := yaml.Unmarshal([]byte(res.Stdout), &raw); err != nil {
+		t.Fatalf("stdout is not valid YAML: %v", err)
+	}
+
+	if _, ok := raw["responses"]; !ok {
+		t.Error("expected 'responses' key in YAML output")
+	}
+	if _, ok := raw["total"]; !ok {
+		t.Error("expected 'total' key in YAML output")
+	}
+}
+
+func TestYAMLOutputHasStatFields(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "yaml")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "count:")
+	assertContains(t, res.Stdout, "min:")
+	assertContains(t, res.Stdout, "max:")
+	assertContains(t, res.Stdout, "average:")
+	assertContains(t, res.Stdout, "p90:")
+	assertContains(t, res.Stdout, "p95:")
+	assertContains(t, res.Stdout, "p99:")
+}
+
+// --- Table output content verification ---
+
+func TestTableOutputContainsHeaders(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "table")
+	assertExitCode(t, res, 0)
+
+	// Table should contain column headers
+	assertContains(t, res.Stdout, "Response")
+	assertContains(t, res.Stdout, "Count")
+	assertContains(t, res.Stdout, "Min")
+	assertContains(t, res.Stdout, "Max")
+}
+
+func TestTableOutputContainsStatusCode(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "table")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "200")
+}
+
+// --- Version output format ---
+
+func TestVersionOutputFormat(t *testing.T) {
+	t.Parallel()
+
+	res := run("-v")
+	assertExitCode(t, res, 0)
+
+	lines := strings.Split(strings.TrimSpace(res.Stdout), "\n")
+	if len(lines) < 4 {
+		t.Fatalf("expected at least 4 lines in version output, got %d: %s", len(lines), res.Stdout)
+	}
+	assertContains(t, lines[0], "Version:")
+	assertContains(t, lines[1], "Git Commit:")
+	assertContains(t, lines[2], "Build Date:")
+	assertContains(t, lines[3], "Go Version:")
+}
diff --git a/e2e/proxy_test.go b/e2e/proxy_test.go
new file mode 100644
index 0000000..6e5ec84
--- /dev/null
+++ b/e2e/proxy_test.go
@@ -0,0 +1,103 @@
+package e2e
+
+import (
+	"testing"
+)
+
+// Note: We can't easily test actual proxy connections in E2E tests without
+// setting up real proxy servers. These tests verify the validation and
+// error handling around proxy configuration.
+
+func TestProxyValidSchemes(t *testing.T) {
+	t.Parallel()
+
+	// Valid proxy scheme should not cause a validation error
+	// (will fail at connection time since no proxy is running, but should pass validation)
+	for _, scheme := range []string{"http", "https", "socks5", "socks5h"} {
+		t.Run(scheme, func(t *testing.T) {
+			t.Parallel()
+
+			res := run("-U", "http://example.com", "-r", "1", "-z", "-q", "-o", "json",
+				"-X", scheme+"://127.0.0.1:9999")
+			assertExitCode(t, res, 0)
+
+			out := res.jsonOutput(t)
+			assertHasResponseKey(t, out, "dry-run")
+		})
+	}
+}
+
+func TestProxyInvalidScheme(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-q", "-o", "json",
+		"-X", "ftp://proxy.example.com:8080")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestMultipleProxiesDryRun(t *testing.T) {
+	t.Parallel()
+
+	// Multiple proxies with dry-run to verify they're accepted
+	res := run("-U", "http://example.com", "-r", "3", "-z", "-q", "-o", "json",
+		"-X", "http://127.0.0.1:8080",
+		"-X", "http://127.0.0.1:8081")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertResponseCount(t, out, 3)
+}
+
+func TestProxyConnectionFailure(t *testing.T) {
+	t.Parallel()
+
+	// Use a proxy that doesn't exist — should get a connection error
+	res := run("-U", "http://example.com", "-r", "1", "-q", "-o", "json",
+		"-X", "http://127.0.0.1:1")
+	// The process should still exit (may exit 0 with error in output or exit 1)
+	if res.ExitCode == 0 {
+		out := res.jsonOutput(t)
+		// Should NOT get a 200 — should have a proxy error
+		if _, ok := out.Responses["200"]; ok {
+			t.Error("expected proxy connection error, but got 200")
+		}
+	}
+}
+
+func TestProxyFromConfigFile(t *testing.T) {
+	t.Parallel()
+
+	config := `
+url: "http://example.com"
+requests: 1
+quiet: true
+output: json
+dryRun: true
+proxy:
+  - http://127.0.0.1:8080
+`
+	configPath := writeTemp(t, "proxy_config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "dry-run")
+}
+
+func TestProxyFromEnv(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "1",
+		"SARIN_DRY_RUN":  "true",
+		"SARIN_OUTPUT":   "json",
+		"SARIN_PROXY":    "http://127.0.0.1:8080",
+	}, "-q")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "dry-run")
+}
diff --git a/e2e/request_test.go b/e2e/request_test.go
new file mode 100644
index 0000000..6180641
--- /dev/null
+++ b/e2e/request_test.go
@@ -0,0 +1,331 @@
+package e2e
+
+import (
+	"net/http"
+	"slices"
+	"testing"
+)
+
+func TestMethodGET(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Method != http.MethodGet {
+		t.Errorf("expected default method GET, got %s", req.Method)
+	}
+}
+
+func TestMethodPOST(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Method != http.MethodPost {
+		t.Errorf("expected method POST, got %s", req.Method)
+	}
+}
+
+func TestMethodExplicit(t *testing.T) {
+	t.Parallel()
+	methods := []string{"GET", "POST", "PUT", "DELETE", "PATCH", "HEAD", "OPTIONS"}
+	for _, method := range methods {
+		t.Run(method, func(t *testing.T) {
+			t.Parallel()
+			cs := newCaptureServer()
+			defer cs.Close()
+
+			res := run("-U", cs.URL, "-r", "1", "-M", method, "-q", "-o", "json")
+			assertExitCode(t, res, 0)
+
+			req := cs.lastRequest()
+			if req.Method != method {
+				t.Errorf("expected method %s, got %s", method, req.Method)
+			}
+		})
+	}
+}
+
+func TestMultipleMethods(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// With multiple methods, sarin cycles through them
+	res := run("-U", cs.URL, "-r", "4", "-M", "GET", "-M", "POST", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	reqs := cs.allRequests()
+	if len(reqs) != 4 {
+		t.Fatalf("expected 4 requests, got %d", len(reqs))
+	}
+
+	// Should see both GET and POST used
+	methods := make(map[string]bool)
+	for _, r := range reqs {
+		methods[r.Method] = true
+	}
+	if !methods["GET"] || !methods["POST"] {
+		t.Errorf("expected both GET and POST to be used, got methods: %v", methods)
+	}
+}
+
+func TestSingleHeader(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-H", "X-Custom: hello", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	vals, ok := req.Headers["X-Custom"]
+	if !ok {
+		t.Fatalf("expected X-Custom header, got headers: %v", req.Headers)
+	}
+	if len(vals) != 1 || vals[0] != "hello" {
+		t.Errorf("expected X-Custom: [hello], got %v", vals)
+	}
+}
+
+func TestMultipleHeaders(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1",
+		"-H", "X-First: one",
+		"-H", "X-Second: two",
+		"-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-First"]; len(v) == 0 || v[0] != "one" {
+		t.Errorf("expected X-First: one, got %v", v)
+	}
+	if v := req.Headers["X-Second"]; len(v) == 0 || v[0] != "two" {
+		t.Errorf("expected X-Second: two, got %v", v)
+	}
+}
+
+func TestHeaderWithEmptyValue(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Header without ": " separator should have empty value
+	res := run("-U", cs.URL, "-r", "1", "-H", "X-Empty", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if _, ok := req.Headers["X-Empty"]; !ok {
+		t.Errorf("expected X-Empty header to be present, got headers: %v", req.Headers)
+	}
+}
+
+func TestDefaultUserAgentHeader(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	ua, ok := req.Headers["User-Agent"]
+	if !ok || len(ua) == 0 {
+		t.Fatalf("expected User-Agent header, got headers: %v", req.Headers)
+	}
+	assertContains(t, ua[0], "Sarin/")
+}
+
+func TestCustomUserAgentOverridesDefault(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-H", "User-Agent: MyAgent/1.0", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	ua := req.Headers["User-Agent"]
+	if len(ua) == 0 {
+		t.Fatal("expected User-Agent header")
+	}
+	// When user sets User-Agent, the default should not be added
+	if slices.Contains(ua, "MyAgent/1.0") {
+		return // found the custom one
+	}
+	t.Errorf("expected custom User-Agent 'MyAgent/1.0', got %v", ua)
+}
+
+func TestSingleParam(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-P", "key1=value1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	vals, ok := req.Query["key1"]
+	if !ok {
+		t.Fatalf("expected key1 param, got query: %v", req.Query)
+	}
+	if len(vals) != 1 || vals[0] != "value1" {
+		t.Errorf("expected key1=[value1], got %v", vals)
+	}
+}
+
+func TestMultipleParams(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1",
+		"-P", "a=1",
+		"-P", "b=2",
+		"-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Query["a"]; len(v) == 0 || v[0] != "1" {
+		t.Errorf("expected a=1, got %v", v)
+	}
+	if v := req.Query["b"]; len(v) == 0 || v[0] != "2" {
+		t.Errorf("expected b=2, got %v", v)
+	}
+}
+
+func TestParamsFromURL(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Params in the URL itself should be extracted and sent
+	res := run("-U", cs.URL+"?fromurl=yes", "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Query["fromurl"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected fromurl=yes from URL query, got %v", v)
+	}
+}
+
+func TestParamsFromURLAndFlag(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Both URL params and -P params should be sent
+	res := run("-U", cs.URL+"?fromurl=yes", "-r", "1", "-P", "fromflag=also", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Query["fromurl"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected fromurl=yes, got %v", v)
+	}
+	if v := req.Query["fromflag"]; len(v) == 0 || v[0] != "also" {
+		t.Errorf("expected fromflag=also, got %v", v)
+	}
+}
+
+func TestSingleCookie(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-C", "session=abc123", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Cookies["session"]; !ok || v != "abc123" {
+		t.Errorf("expected cookie session=abc123, got cookies: %v", req.Cookies)
+	}
+}
+
+func TestMultipleCookies(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1",
+		"-C", "session=abc",
+		"-C", "token=xyz",
+		"-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Cookies["session"]; !ok || v != "abc" {
+		t.Errorf("expected cookie session=abc, got %v", req.Cookies)
+	}
+	if v, ok := req.Cookies["token"]; !ok || v != "xyz" {
+		t.Errorf("expected cookie token=xyz, got %v", req.Cookies)
+	}
+}
+
+func TestBody(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-B", "hello world", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "hello world" {
+		t.Errorf("expected body 'hello world', got %q", req.Body)
+	}
+}
+
+func TestBodyJSON(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	jsonBody := `{"name":"test","value":42}`
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-B", jsonBody, "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != jsonBody {
+		t.Errorf("expected body %q, got %q", jsonBody, req.Body)
+	}
+}
+
+func TestURLPath(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL+"/api/v1/users", "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Path != "/api/v1/users" {
+		t.Errorf("expected path /api/v1/users, got %s", req.Path)
+	}
+}
+
+func TestParamWithEmptyValue(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Param without = value
+	res := run("-U", cs.URL, "-r", "1", "-P", "empty", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if _, ok := req.Query["empty"]; !ok {
+		t.Errorf("expected 'empty' param to be present, got query: %v", req.Query)
+	}
+}
diff --git a/e2e/script_errors_test.go b/e2e/script_errors_test.go
new file mode 100644
index 0000000..c248983
--- /dev/null
+++ b/e2e/script_errors_test.go
@@ -0,0 +1,137 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestJsScriptModifiesPath(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) { req.path = "/js-modified"; return req; }`
+	scriptPath := writeTemp(t, "modify_path.js", script)
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json", "-js", "@"+scriptPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Path != "/js-modified" {
+		t.Errorf("expected path /js-modified from JS script, got %s", req.Path)
+	}
+}
+
+func TestJsScriptRuntimeError(t *testing.T) {
+	t.Parallel()
+
+	// This script throws an error at runtime
+	script := `function transform(req) { throw new Error("runtime boom"); }`
+
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json", "-js", script)
+	assertExitCode(t, res, 0)
+
+	// The request should fail with a script error, not a 200
+	out := res.jsonOutput(t)
+	if _, ok := out.Responses["200"]; ok {
+		t.Error("expected script runtime error, but got 200")
+	}
+}
+
+func TestLuaScriptRuntimeError(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Script that will error at runtime
+	script := `function transform(req) error("lua runtime boom") end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json", "-lua", script)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	if _, ok := out.Responses["200"]; ok {
+		t.Error("expected script runtime error, but got 200")
+	}
+}
+
+func TestJsScriptReturnsNull(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// transform returns null instead of object
+	script := `function transform(req) { return null; }`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json", "-js", script)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	if _, ok := out.Responses["200"]; ok {
+		t.Error("expected error for null return, but got 200")
+	}
+}
+
+func TestJsScriptReturnsUndefined(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// transform returns nothing (undefined)
+	script := `function transform(req) { }`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json", "-js", script)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	if _, ok := out.Responses["200"]; ok {
+		t.Error("expected error for undefined return, but got 200")
+	}
+}
+
+func TestScriptFromNonexistentFile(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-q", "-o", "json",
+		"-lua", "@/nonexistent/path/script.lua")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+	assertContains(t, res.Stderr, "failed to load script")
+}
+
+func TestScriptFromNonexistentURL(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-q", "-o", "json",
+		"-js", "@http://127.0.0.1:1/nonexistent.js")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+	assertContains(t, res.Stderr, "failed to load script")
+}
+
+func TestMultipleLuaAndJsScripts(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	lua1 := `function transform(req) req.headers["X-Lua-1"] = {"yes"} return req end`
+	lua2 := `function transform(req) req.headers["X-Lua-2"] = {"yes"} return req end`
+	js1 := `function transform(req) { req.headers["X-Js-1"] = ["yes"]; return req; }`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", lua1, "-lua", lua2, "-js", js1)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Lua-1"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-Lua-1: yes, got %v", v)
+	}
+	if v := req.Headers["X-Lua-2"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-Lua-2: yes, got %v", v)
+	}
+	if v := req.Headers["X-Js-1"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-Js-1: yes, got %v", v)
+	}
+}
diff --git a/e2e/script_test.go b/e2e/script_test.go
new file mode 100644
index 0000000..2635ce3
--- /dev/null
+++ b/e2e/script_test.go
@@ -0,0 +1,392 @@
+package e2e
+
+import (
+	"net/http"
+	"testing"
+)
+
+func TestLuaScriptInline(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) req.headers["X-Lua"] = {"from-lua"} return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Headers["X-Lua"]; !ok || len(v) == 0 || v[0] != "from-lua" {
+		t.Errorf("expected X-Lua: from-lua, got headers: %v", req.Headers)
+	}
+}
+
+func TestJsScriptInline(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) { req.headers["X-Js"] = ["from-js"]; return req; }`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-js", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Headers["X-Js"]; !ok || len(v) == 0 || v[0] != "from-js" {
+		t.Errorf("expected X-Js: from-js, got headers: %v", req.Headers)
+	}
+}
+
+func TestLuaScriptFromFile(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	scriptContent := `function transform(req)
+    req.headers["X-From-File"] = {"yes"}
+    return req
+end`
+	scriptPath := writeTemp(t, "test.lua", scriptContent)
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", "@"+scriptPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Headers["X-From-File"]; !ok || len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-From-File: yes, got headers: %v", req.Headers)
+	}
+}
+
+func TestJsScriptFromFile(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	scriptContent := `function transform(req) {
+    req.headers["X-From-File"] = ["yes"];
+    return req;
+}`
+	scriptPath := writeTemp(t, "test.js", scriptContent)
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-js", "@"+scriptPath)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Headers["X-From-File"]; !ok || len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-From-File: yes, got headers: %v", req.Headers)
+	}
+}
+
+func TestLuaScriptModifiesMethod(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) req.method = "PUT" return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Method != http.MethodPut {
+		t.Errorf("expected method PUT after Lua transform, got %s", req.Method)
+	}
+}
+
+func TestJsScriptModifiesMethod(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) { req.method = "DELETE"; return req; }`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-js", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Method != http.MethodDelete {
+		t.Errorf("expected method DELETE after JS transform, got %s", req.Method)
+	}
+}
+
+func TestLuaScriptModifiesPath(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) req.path = "/modified" return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Path != "/modified" {
+		t.Errorf("expected path /modified, got %s", req.Path)
+	}
+}
+
+func TestLuaScriptModifiesBody(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) req.body = "lua-body" return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-lua", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "lua-body" {
+		t.Errorf("expected body 'lua-body', got %q", req.Body)
+	}
+}
+
+func TestJsScriptModifiesBody(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) { req.body = "js-body"; return req; }`
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-js", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "js-body" {
+		t.Errorf("expected body 'js-body', got %q", req.Body)
+	}
+}
+
+func TestLuaScriptModifiesParams(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) req.params["lua_param"] = {"lua_value"} return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Query["lua_param"]; !ok || len(v) == 0 || v[0] != "lua_value" {
+		t.Errorf("expected lua_param=lua_value, got query: %v", req.Query)
+	}
+}
+
+func TestJsScriptModifiesParams(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) { req.params["js_param"] = ["js_value"]; return req; }`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-js", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Query["js_param"]; !ok || len(v) == 0 || v[0] != "js_value" {
+		t.Errorf("expected js_param=js_value, got query: %v", req.Query)
+	}
+}
+
+func TestLuaScriptModifiesCookies(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) req.cookies["lua_cookie"] = {"lua_val"} return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Cookies["lua_cookie"]; !ok || v != "lua_val" {
+		t.Errorf("expected cookie lua_cookie=lua_val, got cookies: %v", req.Cookies)
+	}
+}
+
+func TestJsScriptModifiesCookies(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) { req.cookies["js_cookie"] = ["js_val"]; return req; }`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-js", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Cookies["js_cookie"]; !ok || v != "js_val" {
+		t.Errorf("expected cookie js_cookie=js_val, got cookies: %v", req.Cookies)
+	}
+}
+
+func TestScriptChainLuaThenJs(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	luaScript := `function transform(req) req.headers["X-Step"] = {"lua"} return req end`
+	jsScript := `function transform(req) { req.headers["X-Js-Step"] = ["js"]; return req; }`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", luaScript,
+		"-js", jsScript)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v, ok := req.Headers["X-Step"]; !ok || len(v) == 0 || v[0] != "lua" {
+		t.Errorf("expected X-Step: lua from Lua script, got %v", req.Headers["X-Step"])
+	}
+	if v, ok := req.Headers["X-Js-Step"]; !ok || len(v) == 0 || v[0] != "js" {
+		t.Errorf("expected X-Js-Step: js from JS script, got %v", req.Headers["X-Js-Step"])
+	}
+}
+
+func TestMultipleLuaScriptsChained(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	lua1 := `function transform(req) req.headers["X-First"] = {"1"} return req end`
+	lua2 := `function transform(req) req.headers["X-Second"] = {"2"} return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", lua1,
+		"-lua", lua2)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-First"]; len(v) == 0 || v[0] != "1" {
+		t.Errorf("expected X-First: 1, got %v", v)
+	}
+	if v := req.Headers["X-Second"]; len(v) == 0 || v[0] != "2" {
+		t.Errorf("expected X-Second: 2, got %v", v)
+	}
+}
+
+func TestScriptWithEscapedAt(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// @@ means the first @ is stripped, rest is treated as inline script
+	script := `@@function transform(req) req.headers["X-At"] = {"escaped"} return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", script)
+	// The @@ prefix strips one @, leaving "@function transform..." which is valid Lua?
+	// Actually no — after stripping the first @, it becomes:
+	// "@function transform(req) ..." which would be interpreted as a file reference.
+	// Wait — the code says: strings starting with "@@" → content = source[1:] = "@function..."
+	// Then it's returned as inline content "@function transform..."
+	// Lua would fail because "@" is not valid Lua syntax.
+	// So this test just validates that the @@ mechanism doesn't crash.
+	// It should fail at the validation step since "@function..." is not valid Lua.
+	assertExitCode(t, res, 1)
+}
+
+func TestLuaScriptMultipleHeaderValues(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	script := `function transform(req) req.headers["X-Multi"] = {"val1", "val2"} return req end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	vals, ok := req.Headers["X-Multi"]
+	if !ok {
+		t.Fatalf("expected X-Multi header, got headers: %v", req.Headers)
+	}
+	if len(vals) != 2 || vals[0] != "val1" || vals[1] != "val2" {
+		t.Errorf("expected X-Multi: [val1, val2], got %v", vals)
+	}
+}
+
+func TestJsScriptCanReadExistingHeaders(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Set a header via CLI, then read it in JS and set a new one based on it
+	script := `function transform(req) {
+		var original = req.headers["X-Original"];
+		if (original && original.length > 0) {
+			req.headers["X-Copy"] = [original[0]];
+		}
+		return req;
+	}`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-H", "X-Original: hello",
+		"-js", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Copy"]; len(v) == 0 || v[0] != "hello" {
+		t.Errorf("expected X-Copy: hello (copied from X-Original), got %v", v)
+	}
+}
+
+func TestLuaScriptCanReadExistingParams(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Set a param via CLI, then read it in Lua
+	script := `function transform(req)
+		local original = req.params["key1"]
+		if original and #original > 0 then
+			req.params["key1_copy"] = {original[1]}
+		end
+		return req
+	end`
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-P", "key1=val1",
+		"-lua", script)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Query["key1_copy"]; len(v) == 0 || v[0] != "val1" {
+		t.Errorf("expected key1_copy=val1 (copied from key1), got %v", v)
+	}
+}
+
+func TestScriptFromHTTPURL(t *testing.T) {
+	t.Parallel()
+
+	// Serve a Lua script via HTTP
+	scriptContent := `function transform(req) req.headers["X-Remote"] = {"yes"} return req end`
+	scriptServer := statusServerWithBody(scriptContent)
+	defer scriptServer.Close()
+
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-lua", "@"+scriptServer.URL)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Remote"]; len(v) == 0 || v[0] != "yes" {
+		t.Errorf("expected X-Remote: yes from remote script, got %v", req.Headers)
+	}
+}
diff --git a/e2e/show_config_extra_test.go b/e2e/show_config_extra_test.go
new file mode 100644
index 0000000..ea8b584
--- /dev/null
+++ b/e2e/show_config_extra_test.go
@@ -0,0 +1,36 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestShowConfigFromYAML(t *testing.T) {
+	t.Parallel()
+	config := `
+url: "http://example.com"
+requests: 1
+showConfig: true
+`
+	configPath := writeTemp(t, "show_config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	// Non-TTY: should output raw YAML config
+	assertContains(t, res.Stdout, "url:")
+	assertContains(t, res.Stdout, "example.com")
+}
+
+func TestShowConfigFromEnv(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":         "http://example.com",
+		"SARIN_REQUESTS":    "1",
+		"SARIN_SHOW_CONFIG": "true",
+	}, "-q")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "url:")
+	assertContains(t, res.Stdout, "example.com")
+}
diff --git a/e2e/show_config_test.go b/e2e/show_config_test.go
new file mode 100644
index 0000000..06868fc
--- /dev/null
+++ b/e2e/show_config_test.go
@@ -0,0 +1,61 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestShowConfigNonTTY(t *testing.T) {
+	t.Parallel()
+
+	// In non-TTY mode (like tests), -s should output raw YAML and exit
+	res := run("-U", "http://example.com", "-r", "1", "-s")
+	assertExitCode(t, res, 0)
+
+	// Should contain YAML-formatted config
+	assertContains(t, res.Stdout, "url:")
+	assertContains(t, res.Stdout, "example.com")
+	assertContains(t, res.Stdout, "requests:")
+}
+
+func TestShowConfigContainsMethod(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-M", "POST", "-s")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "method:")
+	assertContains(t, res.Stdout, "POST")
+}
+
+func TestShowConfigContainsHeaders(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-s",
+		"-H", "X-Custom: test-value")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "X-Custom")
+	assertContains(t, res.Stdout, "test-value")
+}
+
+func TestShowConfigContainsTimeout(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-T", "5s", "-s")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "timeout:")
+}
+
+func TestShowConfigWithEnvVars(t *testing.T) {
+	t.Parallel()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      "http://example.com",
+		"SARIN_REQUESTS": "5",
+	}, "-s")
+	assertExitCode(t, res, 0)
+
+	assertContains(t, res.Stdout, "example.com")
+	assertContains(t, res.Stdout, "requests:")
+}
diff --git a/e2e/signal_test.go b/e2e/signal_test.go
new file mode 100644
index 0000000..4af69d5
--- /dev/null
+++ b/e2e/signal_test.go
@@ -0,0 +1,116 @@
+package e2e
+
+import (
+	"encoding/json"
+	"syscall"
+	"testing"
+	"time"
+)
+
+func TestSIGINTGracefulShutdown(t *testing.T) {
+	t.Parallel()
+	srv := slowServer(100 * time.Millisecond)
+	defer srv.Close()
+
+	// Start a duration-based test that would run for a long time
+	cmd, stdout := startProcess(
+		"-U", srv.URL, "-d", "30s", "-q", "-o", "json",
+	)
+
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("failed to start process: %v", err)
+	}
+
+	// Let it run for a bit so some requests complete
+	time.Sleep(500 * time.Millisecond)
+
+	// Send SIGINT for graceful shutdown
+	if err := cmd.Process.Signal(syscall.SIGINT); err != nil {
+		t.Fatalf("failed to send SIGINT: %v", err)
+	}
+
+	// Wait for process to exit
+	err := cmd.Wait()
+	_ = err // May exit with 0 or non-zero depending on timing
+
+	// Should have produced valid JSON output with partial results
+	output := stdout.String()
+	if output == "" {
+		t.Fatal("expected JSON output after SIGINT, got empty stdout")
+	}
+
+	var out outputData
+	if err := json.Unmarshal([]byte(output), &out); err != nil {
+		t.Fatalf("expected valid JSON after graceful shutdown: %v\nstdout: %s", err, output)
+	}
+
+	count, _ := out.Total.Count.Int64()
+	if count < 1 {
+		t.Errorf("expected at least 1 request before shutdown, got %d", count)
+	}
+}
+
+func TestSIGTERMGracefulShutdown(t *testing.T) {
+	t.Parallel()
+	srv := slowServer(100 * time.Millisecond)
+	defer srv.Close()
+
+	cmd, stdout := startProcess(
+		"-U", srv.URL, "-d", "30s", "-q", "-o", "json",
+	)
+
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("failed to start process: %v", err)
+	}
+
+	time.Sleep(500 * time.Millisecond)
+
+	if err := cmd.Process.Signal(syscall.SIGTERM); err != nil {
+		t.Fatalf("failed to send SIGTERM: %v", err)
+	}
+
+	err := cmd.Wait()
+	_ = err
+
+	output := stdout.String()
+	if output == "" {
+		t.Fatal("expected JSON output after SIGTERM, got empty stdout")
+	}
+
+	var out outputData
+	if err := json.Unmarshal([]byte(output), &out); err != nil {
+		t.Fatalf("expected valid JSON after graceful shutdown: %v\nstdout: %s", err, output)
+	}
+}
+
+func TestSIGINTExitsInReasonableTime(t *testing.T) {
+	t.Parallel()
+	srv := slowServer(50 * time.Millisecond)
+	defer srv.Close()
+
+	cmd, _ := startProcess(
+		"-U", srv.URL, "-d", "60s", "-q", "-o", "none",
+	)
+
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("failed to start process: %v", err)
+	}
+
+	time.Sleep(300 * time.Millisecond)
+
+	if err := cmd.Process.Signal(syscall.SIGINT); err != nil {
+		t.Fatalf("failed to send SIGINT: %v", err)
+	}
+
+	// Should exit within 5 seconds
+	done := make(chan error, 1)
+	go func() { done <- cmd.Wait() }()
+
+	select {
+	case <-done:
+		// Good — exited in time
+	case <-time.After(5 * time.Second):
+		cmd.Process.Kill()
+		t.Fatal("process did not exit within 5 seconds after SIGINT")
+	}
+}
diff --git a/e2e/template_funcs_extra_test.go b/e2e/template_funcs_extra_test.go
new file mode 100644
index 0000000..5f345e3
--- /dev/null
+++ b/e2e/template_funcs_extra_test.go
@@ -0,0 +1,116 @@
+package e2e
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestDictStr(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// dict_Str creates a map; use with index to retrieve a value
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ $d := dict_Str "name" "alice" "role" "admin" }}{{ index $d "name" }}-{{ index $d "role" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "alice-admin" {
+		t.Errorf("expected body alice-admin, got %q", req.Body)
+	}
+}
+
+func TestStringsToDate(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// strings_ToDate parses a date string; verify it produces a non-empty result
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-H", `X-Date: {{ strings_ToDate "2024-06-15" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Date"]; len(v) == 0 || v[0] == "" {
+		t.Error("expected X-Date to have a non-empty value")
+	} else {
+		assertContains(t, v[0], "2024")
+	}
+}
+
+func TestFileBase64NonexistentFile(t *testing.T) {
+	t.Parallel()
+
+	// file_Base64 errors at runtime, the error becomes the response key
+	res := run("-U", "http://example.com", "-r", "1", "-z", "-q", "-o", "json",
+		"-B", `{{ file_Base64 "/nonexistent/file.txt" }}`)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	// Should have a template rendering error as response key, not "dry-run"
+	if _, ok := out.Responses["dry-run"]; ok {
+		t.Error("expected template error, but got dry-run response")
+	}
+	assertResponseCount(t, out, 1)
+}
+
+func TestFileBase64FailedHTTP(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-z", "-q", "-o", "json",
+		"-B", `{{ file_Base64 "http://127.0.0.1:1/nonexistent" }}`)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	if _, ok := out.Responses["dry-run"]; ok {
+		t.Error("expected template error, but got dry-run response")
+	}
+	assertResponseCount(t, out, 1)
+}
+
+func TestMultipleValuesFlags(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-V", "KEY1=val1", "-V", "KEY2=val2",
+		"-H", "X-K1: {{ .Values.KEY1 }}",
+		"-H", "X-K2: {{ .Values.KEY2 }}")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-K1"]; len(v) == 0 || v[0] != "val1" {
+		t.Errorf("expected X-K1: val1, got %v", v)
+	}
+	if v := req.Headers["X-K2"]; len(v) == 0 || v[0] != "val2" {
+		t.Errorf("expected X-K2: val2, got %v", v)
+	}
+}
+
+func TestValuesUsedInBodyAndHeader(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Same value used in both header and body within the same request
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-V", "ID={{ fakeit_UUID }}",
+		"-H", "X-Request-Id: {{ .Values.ID }}",
+		"-B", `{"id":"{{ .Values.ID }}"}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	headerID := ""
+	if v := req.Headers["X-Request-Id"]; len(v) > 0 {
+		headerID = v[0]
+	}
+	if headerID == "" {
+		t.Fatal("expected X-Request-Id to have a value")
+	}
+	// Body should contain the same UUID as the header
+	if !strings.Contains(req.Body, headerID) {
+		t.Errorf("expected body to contain same ID as header (%s), got body: %s", headerID, req.Body)
+	}
+}
diff --git a/e2e/template_funcs_test.go b/e2e/template_funcs_test.go
new file mode 100644
index 0000000..3058e94
--- /dev/null
+++ b/e2e/template_funcs_test.go
@@ -0,0 +1,170 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestStringToUpper(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-H", `X-Upper: {{ strings_ToUpper "hello" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Upper"]; len(v) == 0 || v[0] != "HELLO" {
+		t.Errorf("expected X-Upper: HELLO, got %v", v)
+	}
+}
+
+func TestStringToLower(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-H", `X-Lower: {{ strings_ToLower "WORLD" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Lower"]; len(v) == 0 || v[0] != "world" {
+		t.Errorf("expected X-Lower: world, got %v", v)
+	}
+}
+
+func TestStringReplace(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ strings_Replace "foo-bar-baz" "-" "_" -1 }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "foo_bar_baz" {
+		t.Errorf("expected body foo_bar_baz, got %q", req.Body)
+	}
+}
+
+func TestStringRemoveSpaces(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ strings_RemoveSpaces "hello world foo" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "helloworldfoo" {
+		t.Errorf("expected body helloworldfoo, got %q", req.Body)
+	}
+}
+
+func TestStringTrimPrefix(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ strings_TrimPrefix "hello-world" "hello-" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "world" {
+		t.Errorf("expected body world, got %q", req.Body)
+	}
+}
+
+func TestStringTrimSuffix(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ strings_TrimSuffix "hello-world" "-world" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "hello" {
+		t.Errorf("expected body hello, got %q", req.Body)
+	}
+}
+
+func TestSliceJoin(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ slice_Join (slice_Str "a" "b" "c") ", " }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "a, b, c" {
+		t.Errorf("expected body 'a, b, c', got %q", req.Body)
+	}
+}
+
+func TestStringFirst(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ strings_First "abcdef" 3 }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "abc" {
+		t.Errorf("expected body abc, got %q", req.Body)
+	}
+}
+
+func TestStringLast(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ strings_Last "abcdef" 3 }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "def" {
+		t.Errorf("expected body def, got %q", req.Body)
+	}
+}
+
+func TestStringTruncate(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ strings_Truncate "hello world" 5 }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "hello..." {
+		t.Errorf("expected body 'hello...', got %q", req.Body)
+	}
+}
+
+func TestSliceStr(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{{ slice_Join (slice_Str "a" "b" "c") "-" }}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != "a-b-c" {
+		t.Errorf("expected body a-b-c, got %q", req.Body)
+	}
+}
diff --git a/e2e/template_test.go b/e2e/template_test.go
new file mode 100644
index 0000000..a2f6575
--- /dev/null
+++ b/e2e/template_test.go
@@ -0,0 +1,241 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestTemplateInHeader(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Use a template function that generates a UUID
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-H", "X-Request-Id: {{ fakeit_UUID }}")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	vals, ok := req.Headers["X-Request-Id"]
+	if !ok || len(vals) == 0 {
+		t.Fatalf("expected X-Request-Id header, got headers: %v", req.Headers)
+	}
+	// UUID format: 8-4-4-4-12
+	if len(vals[0]) != 36 {
+		t.Errorf("expected UUID (36 chars), got %q (%d chars)", vals[0], len(vals[0]))
+	}
+}
+
+func TestTemplateInParam(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-P", "id={{ fakeit_UUID }}")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	vals, ok := req.Query["id"]
+	if !ok || len(vals) == 0 {
+		t.Fatalf("expected 'id' param, got query: %v", req.Query)
+	}
+	if len(vals[0]) != 36 {
+		t.Errorf("expected UUID in param value, got %q", vals[0])
+	}
+}
+
+func TestTemplateInBody(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-B", `{"id":"{{ fakeit_UUID }}"}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if len(req.Body) < 36 {
+		t.Errorf("expected body to contain a UUID, got %q", req.Body)
+	}
+	assertContains(t, req.Body, `"id":"`)
+}
+
+func TestTemplateInURLPath(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL+"/api/{{ fakeit_UUID }}", "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if len(req.Path) < 5+36 { // "/api/" + UUID
+		t.Errorf("expected path to contain a UUID, got %q", req.Path)
+	}
+}
+
+func TestValuesBasic(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-V", "MY_VAR=hello",
+		"-H", "X-Val: {{ .Values.MY_VAR }}")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-Val"]; len(v) == 0 || v[0] != "hello" {
+		t.Errorf("expected X-Val: hello from Values, got %v", v)
+	}
+}
+
+func TestValuesMultiple(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-V", "A=first",
+		"-V", "B=second",
+		"-H", "X-A: {{ .Values.A }}",
+		"-H", "X-B: {{ .Values.B }}")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Headers["X-A"]; len(v) == 0 || v[0] != "first" {
+		t.Errorf("expected X-A: first, got %v", v)
+	}
+	if v := req.Headers["X-B"]; len(v) == 0 || v[0] != "second" {
+		t.Errorf("expected X-B: second, got %v", v)
+	}
+}
+
+func TestValuesWithTemplate(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	// Values themselves can contain templates
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-V", "REQ_ID={{ fakeit_UUID }}",
+		"-H", "X-Request-Id: {{ .Values.REQ_ID }}")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	vals, ok := req.Headers["X-Request-Id"]
+	if !ok || len(vals) == 0 {
+		t.Fatalf("expected X-Request-Id header, got %v", req.Headers)
+	}
+	if len(vals[0]) != 36 {
+		t.Errorf("expected UUID from value template, got %q", vals[0])
+	}
+}
+
+func TestValuesInParam(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+		"-V", "TOKEN=abc123",
+		"-P", "token={{ .Values.TOKEN }}")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if v := req.Query["token"]; len(v) == 0 || v[0] != "abc123" {
+		t.Errorf("expected token=abc123, got %v", v)
+	}
+}
+
+func TestValuesInBody(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "1", "-M", "POST", "-q", "-o", "json",
+		"-V", "NAME=test-user",
+		"-B", `{"name":"{{ .Values.NAME }}"}`)
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Body != `{"name":"test-user"}` {
+		t.Errorf("expected body with interpolated value, got %q", req.Body)
+	}
+}
+
+func TestValuesInURLPath(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL+"/users/{{ .Values.USER_ID }}", "-r", "1", "-q", "-o", "json",
+		"-V", "USER_ID=42")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Path != "/users/42" {
+		t.Errorf("expected path /users/42, got %s", req.Path)
+	}
+}
+
+func TestTemplateGeneratesDifferentValues(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL, "-r", "5", "-c", "1", "-q", "-o", "json",
+		"-H", "X-Unique: {{ fakeit_UUID }}")
+	assertExitCode(t, res, 0)
+
+	reqs := cs.allRequests()
+	if len(reqs) < 5 {
+		t.Fatalf("expected 5 requests, got %d", len(reqs))
+	}
+
+	// UUIDs should be unique across requests
+	seen := make(map[string]bool)
+	for _, r := range reqs {
+		vals := r.Headers["X-Unique"]
+		if len(vals) > 0 {
+			seen[vals[0]] = true
+		}
+	}
+	if len(seen) < 2 {
+		t.Errorf("expected template to generate different UUIDs across requests, got %d unique values", len(seen))
+	}
+}
+
+func TestTemplateFunctionFakeit(t *testing.T) {
+	t.Parallel()
+	cs := newCaptureServer()
+	t.Cleanup(cs.Close)
+
+	// Test various fakeit functions
+	tests := []struct {
+		name     string
+		template string
+	}{
+		{"UUID", "{{ fakeit_UUID }}"},
+		{"Name", "{{ fakeit_Name }}"},
+		{"Email", "{{ fakeit_Email }}"},
+		{"Number", "{{ fakeit_Number 1 100 }}"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			cs := newCaptureServer()
+			defer cs.Close()
+
+			res := run("-U", cs.URL, "-r", "1", "-q", "-o", "json",
+				"-H", "X-Test: "+tt.template)
+			assertExitCode(t, res, 0)
+
+			req := cs.lastRequest()
+			if v := req.Headers["X-Test"]; len(v) == 0 || v[0] == "" {
+				t.Errorf("expected non-empty value from %s, got %v", tt.template, v)
+			}
+		})
+	}
+}
diff --git a/e2e/timeout_test.go b/e2e/timeout_test.go
new file mode 100644
index 0000000..dd8200a
--- /dev/null
+++ b/e2e/timeout_test.go
@@ -0,0 +1,110 @@
+package e2e
+
+import (
+	"testing"
+	"time"
+)
+
+func TestRequestTimeout(t *testing.T) {
+	t.Parallel()
+
+	// Server that takes 2 seconds to respond
+	srv := slowServer(2 * time.Second)
+	defer srv.Close()
+
+	// Timeout of 200ms — should fail with timeout error
+	res := run("-U", srv.URL, "-r", "1", "-T", "200ms", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	// Should NOT have "200" — should have a timeout error
+	if _, ok := out.Responses["200"]; ok {
+		t.Error("expected timeout error, but got 200")
+	}
+	// Total count should still be 1 (the timed-out request is counted)
+	assertResponseCount(t, out, 1)
+}
+
+func TestRequestTimeoutMultiple(t *testing.T) {
+	t.Parallel()
+
+	srv := slowServer(2 * time.Second)
+	defer srv.Close()
+
+	res := run("-U", srv.URL, "-r", "3", "-c", "3", "-T", "200ms", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertResponseCount(t, out, 3)
+
+	// None should be 200
+	if _, ok := out.Responses["200"]; ok {
+		t.Error("expected all requests to timeout, but got some 200s")
+	}
+}
+
+func TestTimeoutDoesNotAffectFastRequests(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	// Short timeout but server responds instantly — should succeed
+	res := run("-U", srv.URL, "-r", "3", "-T", "5s", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+	assertResponseCount(t, out, 3)
+}
+
+func TestDurationStopsAfterTime(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	start := time.Now()
+	res := run("-U", srv.URL, "-d", "1s", "-q", "-o", "json")
+	elapsed := time.Since(start)
+
+	assertExitCode(t, res, 0)
+
+	// Should finish roughly around 1s (allow some tolerance)
+	if elapsed < 900*time.Millisecond {
+		t.Errorf("expected test to run ~1s, but finished in %v", elapsed)
+	}
+	if elapsed > 3*time.Second {
+		t.Errorf("expected test to finish around 1s, but took %v", elapsed)
+	}
+}
+
+func TestDurationWithRequestLimit(t *testing.T) {
+	t.Parallel()
+	srv := echoServer()
+	defer srv.Close()
+
+	// Request limit reached before duration — should stop early
+	res := run("-U", srv.URL, "-r", "2", "-d", "30s", "-q", "-o", "json")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertResponseCount(t, out, 2)
+}
+
+func TestDurationWithSlowServerStopsAtDuration(t *testing.T) {
+	t.Parallel()
+
+	// Server delays 500ms per request
+	srv := slowServer(500 * time.Millisecond)
+	defer srv.Close()
+
+	start := time.Now()
+	res := run("-U", srv.URL, "-d", "1s", "-c", "1", "-q", "-o", "json")
+	elapsed := time.Since(start)
+
+	assertExitCode(t, res, 0)
+
+	// Should stop after ~1s even though requests are slow
+	if elapsed > 3*time.Second {
+		t.Errorf("expected to stop around 1s duration, took %v", elapsed)
+	}
+}
diff --git a/e2e/tls_test.go b/e2e/tls_test.go
new file mode 100644
index 0000000..b692b4a
--- /dev/null
+++ b/e2e/tls_test.go
@@ -0,0 +1,164 @@
+package e2e
+
+import (
+	"crypto/tls"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestHTTPSWithInsecureFlag(t *testing.T) {
+	t.Parallel()
+
+	// Create a TLS server with a self-signed cert
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	// Without --insecure, it should fail (cert not trusted)
+	// With --insecure, it should succeed
+	res := run("-U", srv.URL, "-r", "1", "-q", "-o", "json", "-I")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+}
+
+func TestHTTPSWithoutInsecureFails(t *testing.T) {
+	t.Parallel()
+
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	// Without --insecure, should get a TLS error (not a clean 200)
+	res := run("-U", srv.URL, "-r", "1", "-q", "-o", "json")
+	assertExitCode(t, res, 0) // Process still exits 0, but response key is an error
+
+	out := res.jsonOutput(t)
+	// Should NOT have a "200" key — should have a TLS error
+	if _, ok := out.Responses["200"]; ok {
+		t.Error("expected TLS error without --insecure, but got 200")
+	}
+}
+
+func TestHTTPSInsecureViaCLILongFlag(t *testing.T) {
+	t.Parallel()
+
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	// Use the long form flag
+	res := run("-U", srv.URL, "-r", "1", "-q", "-o", "json", "-insecure")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+}
+
+func TestHTTPSInsecureViaConfigFile(t *testing.T) {
+	t.Parallel()
+
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	config := `
+url: "` + srv.URL + `"
+requests: 1
+insecure: true
+quiet: true
+output: json
+`
+	configPath := writeTemp(t, "tls_config.yaml", config)
+
+	res := run("-f", configPath)
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+}
+
+func TestHTTPSInsecureViaEnv(t *testing.T) {
+	t.Parallel()
+
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	res := runWithEnv(map[string]string{
+		"SARIN_URL":      srv.URL,
+		"SARIN_REQUESTS": "1",
+		"SARIN_INSECURE": "true",
+		"SARIN_QUIET":    "true",
+		"SARIN_OUTPUT":   "json",
+	})
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+}
+
+func TestHTTPSEchoServer(t *testing.T) {
+	t.Parallel()
+
+	// TLS echo server that returns request details
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		resp := map[string]any{
+			"method": r.Method,
+			"path":   r.URL.Path,
+			"tls":    r.TLS != nil,
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer srv.Close()
+
+	// Verify request was received over TLS
+	res := run("-U", srv.URL+"/secure-path", "-r", "1", "-q", "-o", "json", "-I")
+	assertExitCode(t, res, 0)
+
+	out := res.jsonOutput(t)
+	assertHasResponseKey(t, out, "200")
+}
+
+// tlsCaptureServer is like captureServer but with TLS
+func tlsCaptureServer() *captureServer {
+	cs := &captureServer{}
+	cs.Server = httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		cs.mu.Lock()
+		cs.requests = append(cs.requests, echoResponse{
+			Method: r.Method,
+			Path:   r.URL.Path,
+		})
+		cs.mu.Unlock()
+		w.WriteHeader(http.StatusOK)
+	}))
+	cs.TLS = &tls.Config{}
+	cs.StartTLS()
+	return cs
+}
+
+func TestHTTPSHeadersSentCorrectly(t *testing.T) {
+	t.Parallel()
+	cs := tlsCaptureServer()
+	defer cs.Close()
+
+	res := run("-U", cs.URL+"/api/test", "-r", "1", "-M", "POST", "-q", "-o", "json", "-I")
+	assertExitCode(t, res, 0)
+
+	req := cs.lastRequest()
+	if req.Method != http.MethodPost {
+		t.Errorf("expected POST over HTTPS, got %s", req.Method)
+	}
+	if req.Path != "/api/test" {
+		t.Errorf("expected path /api/test over HTTPS, got %s", req.Path)
+	}
+}
diff --git a/e2e/validation_extra_test.go b/e2e/validation_extra_test.go
new file mode 100644
index 0000000..ab4194e
--- /dev/null
+++ b/e2e/validation_extra_test.go
@@ -0,0 +1,13 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestValidation_ConcurrencyExceedsMax(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-q", "-c", "200000000")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "concurrency must not exceed 100,000,000")
+}
diff --git a/e2e/validation_test.go b/e2e/validation_test.go
new file mode 100644
index 0000000..8fc40f4
--- /dev/null
+++ b/e2e/validation_test.go
@@ -0,0 +1,168 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestValidation_MissingURL(t *testing.T) {
+	t.Parallel()
+	res := run("-r", "1")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "URL")
+	assertContains(t, res.Stderr, "required")
+}
+
+func TestValidation_InvalidURLScheme(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "ftp://example.com", "-r", "1")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "URL")
+	assertContains(t, res.Stderr, "scheme")
+}
+
+func TestValidation_URLWithoutHost(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://", "-r", "1")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "URL")
+}
+
+func TestValidation_NoRequestsOrDuration(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "request count or duration")
+}
+
+func TestValidation_ZeroRequests(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "0")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "Requests")
+}
+
+func TestValidation_ZeroDuration(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-d", "0s")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "Duration")
+}
+
+func TestValidation_ZeroRequestsAndZeroDuration(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "0", "-d", "0s")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestValidation_ConcurrencyZero(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1", "-c", "0")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "concurrency")
+}
+
+func TestValidation_TimeoutZero(t *testing.T) {
+	t.Parallel()
+	// Timeout of 0 is invalid (must be > 0)
+	res := run("-U", "http://example.com", "-r", "1", "-T", "0s")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "timeout")
+}
+
+func TestValidation_InvalidOutputFormat(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1", "-o", "xml")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "Output")
+}
+
+func TestValidation_InvalidProxyScheme(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1", "-X", "ftp://proxy.example.com:8080")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "proxy")
+}
+
+func TestValidation_EmptyLuaScript(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1", "-lua", "")
+	assertExitCode(t, res, 1)
+}
+
+func TestValidation_EmptyJsScript(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1", "-js", "")
+	assertExitCode(t, res, 1)
+}
+
+func TestValidation_LuaScriptMissingTransform(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1",
+		"-lua", `print("hello")`)
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestValidation_JsScriptMissingTransform(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1",
+		"-js", `console.log("hello")`)
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestValidation_LuaScriptSyntaxError(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1",
+		"-lua", `function transform(req invalid syntax`)
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestValidation_JsScriptSyntaxError(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1",
+		"-js", `function transform(req { invalid`)
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestValidation_ScriptEmptyFileRef(t *testing.T) {
+	t.Parallel()
+	// "@" with nothing after it
+	res := run("-U", "http://example.com", "-r", "1", "-lua", "@")
+	assertExitCode(t, res, 1)
+}
+
+func TestValidation_ScriptNonexistentFile(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1",
+		"-lua", "@/nonexistent/path/script.lua")
+	assertExitCode(t, res, 1)
+}
+
+func TestValidation_InvalidTemplateInHeader(t *testing.T) {
+	t.Parallel()
+	res := run("-U", "http://example.com", "-r", "1",
+		"-H", "X-Test: {{ invalid_func }}")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestValidation_InvalidTemplateInBody(t *testing.T) {
+	t.Parallel()
+	// Use a template with invalid syntax (unclosed action)
+	res := run("-U", "http://example.com", "-r", "1",
+		"-B", "{{ invalid_func_xyz }}")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "VALIDATION")
+}
+
+func TestValidation_MultipleErrors(t *testing.T) {
+	t.Parallel()
+	// No URL, no requests/duration — should report multiple validation errors
+	res := run("-c", "1")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "URL")
+}